What is the Difference Between Azeotropic and Zeotropic Mixtures

Mixtures are combinations of two or more substances that are physically mixed together but not chemically bonded. They can be solid, liquid, or gas. Mixtures can be separated into their individual components. There are different classifications (types) of mixtures. Azeotropic and zeotropic mixtures are two such mixtures.

What is the difference between azeotropic and zeotropic mixture? An azeotropic mixture boils at a constant temperature, while a zeotropic mixture boils over a range of temperatures.

Key Areas Covered

1. What are Azeotropic Mixtures
      – Definition, Features, Applications
2. What are Zeotropic Mixtures
      – Definition, Features, Applications
3. Similarities Between Azeotropic and Zeotropic Mixtures
      – Outline of Common Features
4. Difference Between Azeotropic and Zeotropic Mixtures
      – Comparison of Key Differences
5. FAQ: Azeotropic and Zeotropic Mixtures
      – Answers to Frequently Asked Questions

Key Terms

Azeotropic Mixture, Zeotropic Mixture

What is an Azeotropic Mixture

Azeotropic mixtures have a constant boiling point. This boiling point is typically different from the boiling points of the individual components in the mixture. For example, in a mixture of alcohol and water, alcohol usually boils at a lower temperature than water. However, an ethanol-water azeotrope (around 95.6% ethanol) boils at a specific temperature distinct from either pure alcohol or water.

In azeotropic mixtures the vapor produced during boiling has the exact same composition as the liquid mixture itself. The proportions of components leaving the liquid as vapor are identical to the proportions in the remaining liquid.

Azeotropes cannot be separated by simple distillation due to the constant boiling point and identical vapor-liquid composition. Hence, it is difficult to get pure components from this method, and special techniques are needed to alter the azeotropic composition. Some of these techniques include fractional distillation with additional columns or adding another component.

There are many applications of azeotropes. For example, refrigerants use azeotropic mixtures to acquire the desired boiling point. Ethanol and water form an azeotrope which is found in alcohol.

What is a Zeotropic Mixture

Zeotropic mixtures are the opposite of azeotropic mixtures when it comes to their boiling behavior. Zeotropic mixtures boil over a range of temperatures. This is because each component in the mixture has its own boiling point.

When the temperature rises, the lower boiling point component boils off first, enriching the remaining liquid in the higher boiling point component. Hence, it creates a change in the boiling point and the composition of the vapor produced.

The vapor produced by a zeotropic mixture has a composition different from that of a liquid mixture. Initially, the vapor will be richer in the lower boiling point component. As the temperature increases and the higher boiling point component starts to vaporize, the vapor composition gradually changes.

Zeotropic mixtures are easy to be separated using fractional distillation, due to the difference in boiling points and vapor liquid composition. Furthermore, zeotropic mixtures are mainly used in refrigerants.

Similarities Between Azeotropic and Zeotropic Mixtures

1. Both azeotropic and zeotropic mixtures are physical combinations of two or more substances that retain their individual chemical identities, which means that they are both mixtures.
2. The properties of both mixture types are influenced by the specific components they contain.

Difference Between Azeotropic and Zeotropic Mixtures

Definition

• An azeotropic mixture is a mixture of liquids that maintains a constant boiling point and composition throughout distillation, while a zeotropic mixture is a mixture of liquids with varying boiling points and compositions throughout distillation.

Boiling Temperature

• Azeotropic mixtures boil at a constant temperature different from the boiling points of their individual components, while zeotropic mixtures boil over a range of temperatures.

Vapor

• The vapor produced in azeotropic mixtures has the same composition as the liquid mixture, while the vapor produced in zeotropic mixtures has a different composition than the liquid mixture.

Separation

• Azeotropic mixtures are difficult to separate using simple distillation, whereas zeotropic mixtures are easier to separate using fractional distillation.

Conclusion

Azeotropic and zeotropic mixtures represent two distinct types of mixtures with contrasting boiling behaviors. Azeotropes boil at a constant temperature with identical vapor and liquid composition, while zeotropic mixtures boil over a range of temperatures with a changing vapor composition. This is the main difference between azeotropic and zeotropic mixture.

FAQ: Azeotropic and Zeotropic Mixture

1. What is an example of an azeotropic mixture?

An azeotropic mixture is a mixture of two or more liquids that has a constant boiling point and composition throughout. Ethanol and water, acetone and chloroform, benzene and toluene, nitric acid and water are examples of zeotropic mixtures.

2. What is a zeotropic mixture with examples?

Zeotropic mixtures have components with different boiling points. This means the mixture boils over a range of temperatures, not just one. Examples of zeotropic mixtures include air and refrigerant blends.

3. What is azeotropic mixture also known as?

Azeotropic mixtures are also known as constant boiling mixtures. They are a liquid mixture that has a constant boiling point and composition throughout the boiling process.

4. Are azeotropic mixtures ideal?

Azeotropic mixture does not obey Raoul’s law, which describes the vapor pressure of an ideal solution, emphasizing the relationship between the vapor pressure of each component in the solution and its mole fraction.  Therefore, they cannot be considered ideal solutions.

5. What are the advantages of azeotropic mixtures?

There are many advantages of azeotropic mixtures. Some of them are efficient separation, safety enhancement (azeotropes can combine a flammable and a non-flammable component to create a safer, non-flammable mixture), and easy recycling.

Reference:

1. “Azeotrope.” Wikipedia. Wikipedia Foundation.
2. “Zeotropic Mixture.” Wikipedia. Wikipedia Foundation. 

Image Courtesy:

1. “VLEIsoropanolWaterAzeotrope” By WilfriedC – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Binary Boiling Point Diagram new” By Derivative work: Michbich (talk) – Binary_Boiling_Point_Diagram.PNG (CC BY-SA 2.5) via Commons Wikimedia